1. Field of the Invention
This invention relates to a piezoelectric actuator and a method of manufacturing the same, particularly to a stacked piezoelectric actuator in which a vertical effect is utilized and a method of manufacturing the same.
2. Description of the Prior Art
A piezoelectric actuator, in which an electrostrictive effect element for transducing electric energy into mechanical energy is utilized, is now used in technological fields such as a mass flow controller, a XY table drive, an injection molding machine and the like.
FIG. 1 shows a longitudinal sectional view of an embodiment of a prior piezoelectric actuator which is received in a metal case.
In this prior art, lead wires 4a and 4b which were drawn from an electrostrictive effect element 1, wherein electrostrictive materials and internal electrodes were stacked by turns, were connected to hermetically sealed lead terminals 2a and 2b sealed with glass 2c, respectively, mounted on a metal member 3 with solder and thereafter the one end face 1a of the electrostrictive effect element 1 is adhered to a concave portion of the metal member 3 with an adhesive such as an epoxy resin or the like. Then, an O ring obtained by molding a resin such as Byton or the like is inserted into a ring channel provided on the periphery of the metal member 3 and thereafter the electrostrictive effect element 1 is inserted into the case 9 through an opening 9a of a cylindrical closed-end metal case 9 to the other end face 1b of the element and the end face 1b is adhered and fixed to the bottom 9b of the metal case 9 with an adhesive such as an epoxy resin or the like, to accomplish the piezoelectric actuator having a hermetically sealed structure.
The prior piezoelectric actuator as mentioned above has such a structure that the electrostrictive effect element is sealed with a contact pressure due to the O ring and as a result there are the following drawbacks in the prior piezoelectric actuator:
(1) Because tensile strength of the electrostrictive effect element in the stacking direction thereof is weak, the element is broken when the tensile force is applied to the stacking direction from the outside in assembling the element.
(2) The electrostrictive effect element is broken when the element is pressed through the metal member in a direction perpendicular to the stacking direction of the element by external force.
In addition, U.S. Pat. No. 4,460,842 discloses means for giving a preload by a cut-in armored case. In the prior art, however, it is impossible to accomplish a hermetic sealing with the means. GB 2087659 and Japanese Utility Registration Public Disclosure Nos. 39664/1989 and 92156/1989 disclose the use of a bellows case but do not preloaded bellows.